“No man who fights with gods will live long or hear his children prattling about his knees when he returns from battle.”
V. 407–409 (tr. Samuel Butler).
Iliad (c. 750 BC)
Original
Ὅττι μάλ' οὐ δηναιὸς ὃς ἀθανάτοισι μάχηται, οὐδέ τί μιν παῖδες ποτὶ γούνασι παππάζουσιν ἐκ πολέμοιο καὶ αἰνῆς δηϊοτῆτος.
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Homér 217
Ancient Greek epic poet, author of the Iliad and the OdysseyRelated quotes

Upon visiting the grave of Johann de Kalb, some years after his death, as quoted in "Baron De Kalb" https://books.google.com/books?id=40wyAQAAMAAJ&pg=PA96&dq=%22Would+to+God+he+had+lived+to+share+its+fruits%22&hl=en&sa=X&ei=2IoZVa3XLuyasQTXiIDoCg&ved=0CB0Q6AEwAA#v=onepage&q=%22Would%20to%20God%20he%20had%20lived%20to%20share%20its%20fruits%22&f=false (1827), by George R. Graham and Edgar Allan Poe, Graham's Illustrated Magazine of Literature, Romance, Art, and Fashion, Volume 2, Watson, p. 96.
Posthumous attributions

“A man is never as big as when he is on his knees to help a child.”

"Song" in The Port Folio Vol. 1, No. 1 (11 January 1806), p. 79; also in Poems of the Late Francis Scott Key, Esq. (1857), p. 34.
Context: When the warrior returns, from the battle afar,
To the home and the country he nobly defended,
O! warm be the welcome to gladden his ear,
And loud be the joy that his perils are ended:
In the full tide of song let his fame roll along,
To the feast-flowing board let us gratefully throng,
Where, mixed with the olive, the laurel shall wave,
And form a bright wreath for the brows of the brave.

Speech to the Third Army (1944)
Context: Every man is scared in his first battle. If he says he's not, he's a liar. Some men are cowards but they fight the same as the brave men or they get the hell slammed out of them watching men fight who are just as scared as they are. The real hero is the man who fights even though he is scared. Some men get over their fright in a minute under fire. For some, it takes an hour. For some, it takes days. But a real man will never let his fear of death overpower his honor, his sense of duty to his country, and his innate manhood. Battle is the most magnificent competition in which a human being can indulge. It brings out all that is best and it removes all that is base.

The Art of Poetry on a New Plan (1761), vol. ii. p. 147.
The saying "he who fights and runs away may live to fight another day" dates at least as far back as Menander (ca. 341–290 B.C.), Gnomai Monostichoi, aphorism #45: ἀνήρ ὁ ϕɛύγων καὶ ράλίν μαχήɛṯαί (a man who flees will fight again). The Attic Nights (book 17, ch. 21) of Aulus Gellius (ca. 125–180 A.D.) indicates it was already widespread in the second century: "...the orator Demosthenes sought safety in flight from the battlefield, and when he was bitterly taunted with his flight, he jestingly replied in the well-known verse: The man who runs away will fight again".